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Help CenterSquare Steel & Square Pipe / Square Tube，Q195、Q215、Q235B、Q355B/C/D/E、20#、45#、40Cr
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Steel Billet，Main Materials Q195, Q235B, Q355B, 20#, 45#, SS400, A36, S235JR,NegotiableMOQ: 1 Metric Ton
1. Product Overview
Square Tube, full name Square Hollow Section (SHS), is hollow structural steel with equal-side square cross-section. Together with rectangular tube (RHS), they are collectively called square & rectangular hollow sections. It is manufactured from hot/cold rolled steel strip, steel plate or billet via cold forming + high-frequency welding or hot seamless extrusion.
With hollow lightweight structure, it delivers outstanding bending and torsion resistance. Under the same load bearing capacity, it consumes less raw material than solid steel profiles and reduces overall project cost. It supports cutting, bending, stamping, welding and hot-dip galvanizing processing, widely applied in steel structure, mechanical frames, PV brackets, infrastructure and municipal guardrails. ERW welded square tube dominates the market, while seamless square tube is adopted for heavy-load thick-wall projects. It complies with Chinese National Standards GB/T 6728 & GB/T 3094, and international trade standards including ASTM A500, EN 10219, JIS G3475.
2. Product Classification by Manufacturing Process
2.1 ERW High-Frequency Welded Square Tube
Most widely used general type
Available Sizes: Side 10×10mm ~ 300×300mm, wall thickness 0.8–12mm
Process: Strip forming + high-frequency resistance welding, smooth weld seam & high dimensional accuracy
Advantages: High production output, cost-effective, smooth surface, abundant spot goods
Applications: Factory frames, PV supports, guardrails, equipment racks, furniture decoration
2.2 SAW Submerged Arc Welded Thick-Wall Square Tube
For large-size heavy-load structures
Available Sizes: Side 150×150mm ~ 500×500mm, wall thickness 6–25mm
Advantages: Deep weld penetration, superior impact resistance & high structural bearing capacity
Applications: Main beams of large workshops, bridge supports, heavy machinery bases
2.3 Seamless Square Tube
Weld-free, high strength & tight sealing performance
Available Sizes: Side 40×40mm ~ 500×500mm, wall thickness 3–60mm
Process: Hot piercing of round billet followed by cold drawing / hot extrusion, no welding defects
Advantages: Uniform mechanical property, fatigue resistance, no leakage risk
Applications: Hydraulic equipment, vehicle chassis, heavy machinery, high-pressure support frames
3. Standard Dimension Parameters
Side length range: 10×10mm ~ 500×500mm
Wall thickness range: 0.8mm ~ 60mm
Standard fixed length: 6m / 9m / 12m; customized length 3–14m available
Theoretical Weight Formula: Weight per meter (kg/m) = 4 × Side (mm) × Wall Thickness (mm) × 0.00785 Example: 100×100×5mm square tube = 4×100×5×0.00785 = 15.7kg/m
4. Material Grades & International Equivalent Standards
4.1 General Carbon Structural Square Tube (Civil & General Structure)
Grades: Q195, Q215, Q235B (equivalent to S235JR, ASTM A500 Gr.B, SS400, STKR400) Features: Easy welding, good plasticity, cost-effective, preferred for indoor general load-bearing structures
4.2 Low Alloy High Strength Square Tube (Heavy Load & Outdoor Projects)
Grades: Q355B/C/D/E (equivalent to S355JR, ASTM A500 Gr.C, STKR490) Features: High yield strength, excellent low-temperature impact toughness, anti-snow & wind load, suitable for PV, bridges and outdoor factories
4.3 High-Quality Carbon / Alloy Seamless Square Tube (Precision Machinery)
Grades: 20#, 45#, 40Cr; adjustable hardness & strength for heat treatment and high-precision equipment frames
5. Optional Surface Treatment
Black bare tube with anti-rust oil: Original factory finish, for indoor steel structures, lowest cost
Hot-dip galvanized tube: Zinc coating 40–600g/㎡, excellent anti-corrosion for PV brackets, guardrails and coastal projects
Electro-galvanized, painting & baking varnish: For decorative use and equipment housings
Pickling passivation, grinding & polishing: Precision processing and decorative machinery
6. Dimensional & Quality Inspection Standards
6.1 Dimensional Tolerance
Side tolerance ±0.5–1.5mm; wall thickness tolerance ±0.1–0.8mm; straightness ≤2mm/m; qualified end perpendicularity
6.2 Surface Quality
Free of cracks, delamination, blowholes, slag inclusion and weld beads; uniform zinc coating without missing plating for galvanized tubes; slight even oxide scale is acceptable for bare tubes
6.3 Mechanical & Flaw Detection
Tensile, bending and flattening tests for all batches; eddy current & ultrasonic testing available for seamless / thick-wall tubes; impact toughness reports can be provided upon request
6.4 Supporting Quality Documents
Original Mill Test Certificate (MTC), mechanical property report, SGS third-party inspection, CE & ISO certifications, meeting customs clearance and re-inspection requirements for export
7. Application Fields
Steel Construction: Main frames, columns and purlins of factories, warehouses and stadiums
New Energy PV Industry: PV mounting brackets, tracking supports, wind power equipment bases
Municipal & Traffic Engineering: Road guardrails, billboard supports, bridge bracings, bus station shelters
Machinery Manufacturing: Equipment racks, machine tool bases, conveying equipment, forklift frames
Automobile Industry: Truck girders, chassis frames, agricultural machinery supports
Agricultural Infrastructure: Greenhouse frames, breeding shed brackets
Decoration Engineering: Curtain wall keels, door & window frames, storage racks, iron art fences
8. Packaging, Delivery & Foreign Trade Terms
8.1 Packaging Methods
Domestic Shipment: Bundled with steel strips, 1–4 tons per bundle; labels marked with specification & material attached outside each bundle
Sea Export Shipment: Anti-rust oil coated, wrapped with inner anti-rust paper + outer waterproof plastic film; large sizes fixed on wooden pallets with edge protectors to avoid collision damage. Compatible with 40GP/40HC containers, mixed loading with other steel sections supported
8.2 Delivery Lead Time
Standard in-stock specifications: 5–7 working days; customized hot-dip galvanized, seamless & extra-thick wall tubes: 7–15 working days
8.3 MOQ & Payment Terms
Minimum Order Quantity: 5 tons; 30% TT advance payment, balance remitted against copy of Bill of Lading; Letter of Credit (LC) is not accepted
8.4 Quality Warranty
Batch inspection on dimension, material and mechanical properties before delivery; 6-month quality warranty, free return & replacement for unqualified material, welds or dimensions under non-human damage conditions
9. Applicable Standards Summary
Chinese National Standards: GB/T 6728-2025 Cold Formed Structural Steel, GB/T 3094 Cold Drawn Seamless Special Shaped Steel Tube International Standards: EN 10219, ASTM A500, JIS G3475
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